die Erfüllung
fulfillment
The realization or achievement of a wish, dream, hope, or promise.
Die Reise nach Japan war für ihn die Erfüllung eines Lebenstraums.
The trip to Japan was the fulfillment of a lifelong dream for him.

fulfillment
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fulfillment
The realization or achievement of a wish, dream, hope, or promise.
Die Reise nach Japan war für ihn die Erfüllung eines Lebenstraums.
The trip to Japan was the fulfillment of a lifelong dream for him.

'Die Erfüllung' (fulfillment) is the nominalization of the verb 'erfüllen' (to fulfill). The noun describes the result or state when a wish, task, or duty is fulfilled.
Er hat sich seinen größten Wunsch erfüllt.
He fulfilled his greatest wish.
For wishes, dreams, or predictions, the fixed expression 'in Erfüllung gehen' (to come true) is often used. It means that they become reality.
Ich hoffe, dass all deine Wünsche in Erfüllung gehen.
I hope all your wishes come true.
To express that someone finds satisfaction in an activity, German uses the construction 'Erfüllung in etwas (Dativ) finden' (to find fulfillment in something).
Viele Menschen finden Erfüllung in ehrenamtlicher Arbeit.
Many people find fulfillment in volunteer work.
In the meaning of 'carrying out a duty', 'Erfüllung' (fulfillment) is used mainly in formal, business, or legal contexts.
Die Erfüllung der Vertragsbedingungen ist für beide Seiten bindend.
The fulfillment of the contractual conditions is binding for both parties.
happiness / luck
'das Glück' and 'die Erfüllung' can both describe a very positive inner state. 'Glück' is more general: you can feel happy because something nice happens or because you are content. 'Erfüllung' sounds deeper and more long-term. It fits especially when a wish comes true or when an activity gives life meaning. So you can feel happiness in a moment, but you are more likely to experience fulfillment through something meaningful. 'Glück' can be used more broadly in everyday language, while 'Erfüllung' is more precise for life goals, work, love, or dreams.

In ihrer Arbeit mit Kindern findet sie echte Erfüllung.
She finds true fulfillment in her work with children.
Nach der guten Nachricht konnte Anna ihr Glück kaum fassen.
After the good news, Anna could hardly believe her happiness.